In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities. Ion implantation systems are often utilized to dope a workpiece, such as a semiconductor wafer, with ions from an ion beam, in order to either produce n- or p-type material doping, or to form passivation layers during fabrication of an integrated circuit. Such beam treatment is often used to selectively implant the wafers with impurities of a specified dopant material, at a predetermined energy level, and in controlled concentration, to produce a semiconductor material during fabrication of an integrated circuit. When used for doping semiconductor wafers, the ion implantation system injects a selected ion species into the workpiece to produce the desired extrinsic material. Implanting ions generated from source materials such as antimony, arsenic, or phosphorus, for example, results in an “n-type” extrinsic material wafer, whereas a “p-type” extrinsic material wafer often results from ions generated with source materials such as boron, gallium, or indium.
A typical ion implanter includes an ion source, an ion extraction device, a mass analysis device, a beam transport device and a wafer processing device. The ion source generates ions of desired atomic or molecular dopant species. These ions are extracted from the source by an extraction system, typically a set of electrodes, which energize and direct the flow of ions from the source, forming an ion beam. Desired ions are separated from the ion beam in a mass analysis device, typically a magnetic dipole performing mass dispersion or separation of the extracted ion beam. The beam transport device, typically a vacuum system containing a series of focusing devices, transports the ion beam to the wafer processing device while maintaining desired properties of the ion beam. Finally, semiconductor wafers are transferred in to and out of the wafer processing device via a wafer handling system, which may include one or more robotic arms, for placing a wafer to be treated in front of the ion beam and removing treated wafers from the ion implanter.
Graphite liners are commonly used throughout the ion implanter for a plurality of reasons, one of the most common being to shield the vacuum system from being struck and damaged by the ion beam. Graphite liners are commonly placed in the vicinity of the wafer plane, and are versatile, in that they can be produced with high purity and manufactured into complex shapes that allow the beamline to be designed free from constraints imposed by the liner material.
Graphite liners, however, tend to suffer from several inherent issues. For example, graphite material can be eroded from the graphite liner by the ion beam, thus causing a need for frequent replacement. Such erosion of the graphite liner may arise through physical or chemically-enhanced sputtering, or through thermal ion beam milling. Further, the graphite liner can be coated by back-sputtered material from the target substrate or from other terminating surfaces (e.g., a tuning Faraday) struck by the ion beam. Such coatings tend to develop a film of material that will, over time, delaminate and cause particle excursions on the workpiece.
Conventionally, such problems are mitigated by densifying surfaces of the graphite liner in an effort to improve a lifetime of the graphite liner. However, such a densification of the surfaces generally does not reduce the amount of material liberated from the surfaces. Other conventional mitigations include roughening the surface(s) through mechanical means. However, such roughening is not usable on all surfaces, and can further result in particles being trapped in the roughened surface.